Telephone system



c; D. KOECHLING TELEPHONE SYSTEM Jan. 5, 1932 '7 Sheets-Sheet I FiledMarch 24, 1930 v t m m 3 INVENTUR Em M3 at Em m m m ATTORNEY Jan. 5,1932.

c. D. KOECZHLING TELEPHONE SYSTEM Filed March 24, 1930 7 Sheets-Sheet 2IHI' I! m L 3 /N VENTUR v C. D. KDEGHL/NG W @444 v A TTURNEY C D.KOECHLING TELEPHONE SYSTEM Jan. 5, 1932.

7 Sheets-Sheet 3 Filed March 24, 1930 //v l/ENTOR G [2 KOECHL/NG 7. 6W4

ATTURNEY Jam 1932. c. D. KOECHLING 1,840,109

TELEPHONE SYSTEM Filed March 24, 1950 7 Sheets-Sheet 4 v k L L I H a VlNl/EA/TUR C1D. KUEGHL/NG' ATTORNEY .I:=\n. 5, 1932. c. D. KOECHLINGTELEPHONE SYSTEM 7 Sheets-Sheet 5 Filed March 24, 1950 /N VENTUR Ci 0KaEc'HL/Ns WFM A rmRA/Ev Jan. 1932. 1 c. b. KOECHLING TELEPHONE SYSTEMFiled March 24, 1930 7 Sheets-Sheet. 6

. INVENTQR C! D. KUECHL/NG 5) WWI "(M ATTORNEY-f Jan. 5, 1932. c. D.KOECHLIQG 1,840,109

TELEPHONE SYSTEM Filed March 24, 1930 7 Sheets-Sheet 7 WW/W A TTURNEYPatented Jan. 5, 1932 UNITED STATES PA E T OFFICE CHARLES n. KOECHIiiNG,or BaooKLYN, NEW yonnnssienon TO BELL mnnnrnonn LABORATORIES,mcoarcnarnn, or-nnw YORK, N. Y., A CORPORATION or NEW YORK 'rnnnrnonn ISYSTEM Application filedMarch 24, 1930. Serial lia 438,255.

This invention relates'to telephone sys tems and particularly toautomaticprivate branch exchange systems.

The object of theinvention is to simplify the intercommunication betweensubscribers and the handling of connections with central ofiicesuHeretofore systems have been employed in which automatic switches may beactuated by impulses to select certain terminalsand thereby causerelays'to be operated to connect calling subscribers lines with thedesired subscribers lines over paths excluding the switches. Systemshavealso been used in which the selection in this manner of oertainterminals causes hunting switches associated with idle trunks to beactuated to establish connections between the trunks andthe callingsubscribers lines over paths excluding the originally operated switches.

A feature of the present invention is a system in which a switchassociated with each subscribers line'is'employed as a marking switchfor calls between subscribers in the private branch exchange, for callsoutgoing and incoming over trunks and calls incoming over trunksoriginally answered by one subscriber and where-this subscribers line isreleased from the trunk and the call then answered another subscriber.

Another feature is a system of this type in which, in the case of a callincoming overa trunk, the subscriber first answering the call may,either by pressing a button'or by dialing certainnumber, cause his lineto be disconnected from this trunk and the trunk marked and held so thatanother subscriber may answer the call over this trunk. The secondsubscriber may then dial a certain number causing the switch associatedwith his line to select a certain terminal and thereby in turn cause aswitch associated with the marked trunk to hunt for and connect thesecond subscribersline with this trunk over a path excluding said secondsubscribers switch.

Another feature is a system of this type in which the switch associatedwith a calling subscribers line may also be employed as the actualconnecting switch between. two

subscribers, or between-a subscriber and a trunk for the above mentioneddifferent kinds of calls. I

This invention has been illustrated in accompany'ing drawings where theFigures 1 to? may be arrangedasshown in Figs. 8, 9

and 10. If the figures are arranged as shown in Fig. 8, Figs. 1 andQ-m'ay be connected together for extension of local calls between twoprivate branch exchange subscribers with the relay system as shown inFig. 2, and for extension of calls of three different kinds, incomingcalls, outgoing calls, and calls transferred from subscriber to anotherusing the transfer key at the subscribers station from which the call isto be transferred. If Figs. 3 and 2 are connected together the sametypes of calls maybe extended over; this circuit with .the

exception that thetransfer'of a call from one subscriber to another isaccomplished by means of dialing from the first called sub-. scribersstation. If Fig. 1 or 3 is connected with Figsle and 5 as shown in Fig.9 the same types of calls may be established with the exception that thelocalcalls are estab-] lished over'switches as shown in Figs. 4 and 5instead of by means of the'relay arrangement shown in Fig. 2. Figs. 6and 7 are connected together as shown in Fig. 10 and the same typesof-calls may be established with the selector connector switch as shownin Fig. 6 used in place of the line switches employedin the previouscircuits for marking the various kinds of connections. In these lattercircuits not only the markin is done by means of the selector connectorbut the final connections are established over the same switch. Thetransfer of a call from one subscriber to another is accom plished bymeans of the operation of a key at the first called subscribers station.

Detailed descriptions will now be made of these various types of callswith the drawings arranged as shown in Figs. 8, 9 and 10.

I my

over the connection established over the subscribers loop through thetip and ring conductors. Relay 201 closes an operating circuit for relay202 as follows: battery, winding of relay 202, armature and frontcontact of relay 201, normal contact and brush of bank 208 to ground atouter right hand armature and back contact of relay 203. Relay 202 inturn closes a circuit for relay 203 to prepare the pulsing circuit forthe actuation of the line switch shown at 1. Relay 203 provides anobvious holding circuit for relay 202. The switch 204 has four banks205, 206, 207 and 208 and may be of the ordinary single movement step bystep type having a stepping magnet 209 for advancing the brushes overterminals one step at a time. The first effect of the operation of relay203 willbe to close a connection from a busy tone supply at 211 to thefirst terminal of the bank 206 to make this subscribers line test busy Ito otherswitches associated with other subscribers lines when theyattempt to make connection with this subscribers line.

At each interruption of the dial the relay 201 releases and operates therotary magnet 209. Relay 212 is in series with the circuit for therotary magnet 209 which may be traced from battery, windings of magnet209 and relay 212 in series, upper armature and back contact of relay213, inner righthand armature and frontcontact of relay 203, armatureand back contact of relay 201, to ground at the outer righthand armatureand front contact of relay 203. Relay 202 is slow in releasing so thatthis relay as well as relay 203 will remain operated during pulsing.Relay 212 is also slow to release and will remain operated duringpulsing. The purpose of the operation of relay 212 is to prevent relay213 from operating while the brushes of bank 206-pass over the terminalsrepresenting lines. The terminals of banks 205 and 206 are arranged torepresent connections to the line at positions 1 to 9 and 11 to 16. Whenthe pulsing has ceased the brushes of switch 204 are placed on terminalsidentifying the desired subscribers line, which may in this case bethesubscribefls line at 215, relay 212 will release and thereby closethe circuit for relay 213 as follows: from battery, winding of a relaycorresponding to relay 217 of the circuit equipment associated with thedesired subscriber indicated by box 218, throughv the inner lefthandarmature and back contact of a relay corresponding to relay 203 of saidcircuits and through the normally connected lead 220 through the secondterminal and brush of bank 206, armature and back contact of relay 212,lower winding of relay 213, to ground at the outer lefthand armature andfront contact of relay 208. If this subscribers line had been busy :1connection would have been established from the busy tone sourcecorresponding to source 211, through the inner lefthand armature andfront contact of the relay corresponding to relay 203 over the lead 220,brush of bank 206, armature and back contact of relay 212, lower innerarmature and back contact of relay 213, condenser 222, ring conductor tothe set at 200 of the calling subscriber, to indicate that the linecalled was busy. Relay 213 would in this case not have been operated andthe relay correspondin to relay 217 would not have been operate as thecircuit therefor would have been 0 en at the inner lefthand armature andbac contact of the relay corresponding to relay 203.

Assuming that the desired subscribers line is not busy and the relaycorresponding to relay 217 operates, the desired subscriber will besignalled from the source corresponding to source 225 over a circuitestablished through the relay corresponding to relay 226 and the upperouter armature and front contact of the relay corresponding to relay 217over the tip conductor to the called subscribers station. Relay 213 inoperating connects its upper winding, through its upper inner armatureand front contact, to the brush of bank 205 to establish a circuit forrelay 227' from battery, winding of this relay, the second terminal ofbank 205 and the corresponding brush, through the upper inner armatureand front contact of relay 213 and its u per winding, to ground at theouter lefthan armature and front contact of relay203'. It should benoted at this time that the relay corresponding to relay 217 at thecalled subscribers circuits also caused the operation of the relayscorresponding to relays 202 and 203 to connect the busy tone source tothe normally connected lead 220 to make this subscribers line test busyand that it is maintained busy by having a locking circuit prepared forthe relay corresponding to relay 217 over lead 228 by the operation ofrelay 227. This locking circuit may be traced from ground through thesecond upper armature and front contact of relay 227, lead 229 throughthe armature and back contact of the relay corresponding to the ringingrelay 226, second upper armature and front contact and winding of therelay corresponding to relay 217, to battery. Relay 227 also connectsthe tip and ring conductors from the calling subscribers line at itsupper armatures and front contacts through condensers 231 to leads 230to the called subscribers line at 215. This circuit is, however, not atpresent completed as the relay corresponding to relay 217 is operated tohold the connection through the tip conductor open at its upper outerarmature and back contact.

When the called subscriber answers, the ringing relay corresponding torelay 226 is operated causing the release of the relay corresponding torelay 217 to establish the connection to the calling subscriber throughthe tip conductor overthe leads230. Talking battery is supplied throughthe relay 201 and the relay corresponding to relay 201 at the calledsubscribers circuits and when this latter relay is operated on ther'eleaseof the relay corresponding to relay 217 the relays correspondingto relays 202 and 203 are maintained operated. Conversation between thesubscribers may now take place? When the subscriber at 200 replaces hisreceiver on the hook at the termination of the call, relays 201, 202,203 and 213 are released. At the called subscribers circuits the relayscorresponding to relays 201, 202-and 203 are released. At the callingsubscribers line the release of the above mentioned relayscause acircuitto be completed for the operation of rotary magnet 209 to return theswitch 204 tonormal. This circuit may be traced from battery, windings.of magnet 209 and relay 212, armature and back contact ofmagnet 209terminals of bank 208 to ground at the outer righthand armature and backcontact of relay 203. This circuit is intermittently opened by therotary magnetand thus causes it to automatically operate and releaseuntil the switch'20 l is returned to normal.

If a call is to be made from the subscriber at the private branchexchange to central of fice this may be done by marking a point on lineswitch 20 1. This marking causes a switch such as 100 which isassociated with an outgoing trunk 101 to hunt for the callingsu'bscribers line and connect it to thetrunk. To accomplish this thecalling subscriber 200 may dial a number 07 and the brushes of theswitch 204 will thereby choose the circuits for an outgoing call. Theoperation of the v circuits in Fig. 2 will be identical as herein beforedescribed in regard to the operation of the switch 204. If it is assumedthat the brushes have been placed at position 17 then when the relay 213tests the terminal 17 on bank 206 it will operate from battery at thelower inner armature and back contact of .relay 102 in the trunkconnecting circuit shown in Fig. 1 over armature and back contact ofrelay 103 and lead 233. If all of the trunks are busy the relay 103 willbe operated as hereinafter described and relay 213 will under thesecircumstances be prevented from operating. Relay 103 on the other handapplies a busy tone from the source 104: through the armature and frontcontact of relay 103 over lead 233 to bank 206 and over the circuithereinbefore traced through condenser 222 to the ring side of thecalling subscribers line to indicate that all of 'theoutgoing trunksarebusy.

In regard to the outgoing trunks, each trunk is equipped with a circuitsuch is shown in Fig. 1 for trunk 101 leading to 100 with the eirceptionof there-lays switch 105, 100 and 107 which are shown to indicat howanother trunk connecting circuit is wired of trunks andrelays 105, 106and 107 represent apart of the connecting circuit for the first trunk inthis group, It should be understood that all trunks should havecorresponding relays connected between the two groups of relays 105, 100and 107 and 111, 112 and 113. lf it is assumed that relay213 operatesasthe last trunk in the group is still idle, the upper winding of thisrelay is connected through the brush 205 over a circuit as follows: fromba tery, start relay 114;, upper inner armature and back contact ofrelayllfi, lower armature and back contact of relay 111, through thelower armatures and fro contacts of the correspondin relays orintermediate trunk circuits, and the lower armature and front Contact ofrela 105 through I the winning of relay 108, concuctor 23%, seventeenthterminal and brush of bank 205, upper inner armature and front contactof relay 213 and upper winding of ti is relay, to ground. at the outerlefthand armature and front contact of relay 203. Relays 108 and 11doperate in this circuit. Relay 111 in operating causes a circuit to beclosed for the stepping magnet 118 as follows: battery, winding ofmagnet 118 and its armature and back contact, upper middle armature andback contact of relay 119, upper ari'nature and back contact of relay120, to ground at the upper outer armature and front contact of relay114. This circuit caused the magnet 118 to o crate and in ooeratin itopens its l. L) A own circuit and therefore continues to'step the switchone step at a time over the terminals until the terminal of the callingline is, reached. In this case, therefore, the switch will only take onestep. The operation of relay 108 causes the relay 102 to opcrate andremove the battery connection from lead 233 at bank 206 and at thecorresponding banks of all other line switches to prevent any otherstation from making a trunk call until this call is completed. L ad 235is connected through terr ml 17 the bank 207 to relay 236and to L118lead 237 ior the marking of the calling subscribefs line on switch 100.'One circuit may be traced from battery through the res c 122, lowerinner armature and. from con act of relay 11 1-, inner upper armatureand back contact of relay 111, through the corresponding armatures andfront contacts of the corresponding relays for the intermediate trunkconnecting circuits, including the upper inner armature and frontcontact of relay 105 (if it is assumed that the associated trunks arebusy) conductor 235, terminal 17 and brush of bank 207 lowerouter'armature and front contact of relay 213, conductor 237 the firstterminal and brush of bank 117, lower outer armature and front contactof relay 114, winding of relay 120 to ground; and the other circuit frombattery winding of relay 236 tothc grtnind over the same circuit fromconductor 237. The fu of the relay 236 is to transfer the callinsubscribers conductors from the line circ it to the trunk 101 throughthe banks of switch 109 and to release the line switch. lVhen the brushof bank 117 therefore comes in contact with the terminal which connectedto conductor 237, relay 120 0}]9111105 over the circuithereinbeforetraced. whilerelay will not operate as it is partly shuntedl the circuit through the resistance 122 to battery at the inner lowerarmature and front contact of relay 114. Relay 120 in. operat ng opensthe circuit for the stepping magnet 118 at its armature and back contactand thus causes the switch to stop in this p0. The relay 120 will notoperate as ch passes over the terminals of other lines as it isconnected through the circuits completed to battery through the windingsof the relays of these 1 n l r 1 other lines corresponding to relay 206..lhe

reason why relay 120 will not operate under these circumstances is thatthe resistance of these relays is too high.

Relay 120 besides stopping the switch at the proper point also causesthe relay 119 to operate over a circuit from battery to the winding ofthis relay, armature and front contact of relay 120, upper outerarmature and front contact of relay 114. Relay 119 holds the circuit forthe stepping magnet 118 open and also establishes a direct connection toground for brush 117 through the front contacts closed by its innerupper armature and the upper armature and front contact of relay 114.This direct ground connection now causes the operation of the relay 236and the release of re-ay 120. The relay 119 in operating also locksitself to the ground at relay 114 over its inner upper armature andfront contacts. Relay 114 also causes the operation of relay 123 over acircuit from battery winding of this relay, upper middle armature andfrontcontact of relay 114, to ground at the upper outer armature andback contact of relay 113. Relay 123 in operating signals the centralofiice by establishing a ground connection through resistance 124 to thetip and ring of the trunk at its upper inner and middle armatures andfront con tacts and through the upper outer armature and back contact ofrelay 125 and second upper armature and back contact of relay 115. Thetip side of the trunk is open at the central ofiice until the operatoranswers or if the central oil ice is an automatic otfice until theapparatus'at this office is ready to receive the dial pulses. he methodof receiving the signal at the central. otlice is immaterial as far asthis invention is concerned but when the operator answers or the centraloflice is ready for the reception of dial pulses, 126 will operate overthe connection established through the tip and ring conductors at thecentral oflice. The operation of relay 126 and front contact of relay129. When relafy 115 operates it indicates that the central 0 fice endof the trunk is connected and that the line calling has been found bythe switch 100, as this circuit is not complete until relays 119 and 126have operated. Relay 115 in operating connects the calling line to thecentral office through its two upper armatures and front contacts.

Relay 115 opens the circuit for relay 114 at its inner upper armatureand back contact and rela 114 opens the marking circuit through ank 117.Relay 236, however, is maintained operated as the circuit therefor isnow completed to ground at the armature and front contact of relay 129,upper outer armature and back contact of relay 130, upper outer armatureand front contact of relay 119, and inner lower armature and frontcontact of relay 115 and inner front contacts of relay 119. This groundalso holds relay 119 operated. Relay 123 releases due to the release ofrelay 114 to remove the connection to ground through resistance 124 forthe tip and ring conductors and short circuits relay 126. Relay 126releases relays 127, 128 and 129 but relay 128 in releasing closes acircuit for relay 132 across the tip and ring conductors prepared by therelease of relay 123. Relay 132 in operating closes a circuit for relay133 which in turn closes the ground connection for holding relays 115,119, and 236 operated. Another re ay operated by the operation of relay115 is relay 111. The circuit for this relay may be traced originallyfrom battery, winding of relay 111, lower make-before-break contacts ofrelay 130, lower armatures and front contacts of relay 115, to ground atrelay 129 and later when relay 129 releases to the ground at relay 133.Relay 111 is also held operated by the holding circuit established byrelay 132. Relay 111 in operating transfers the start lead 235 and thelead 234 to the next trunk, provided of course that the last trunk. isnot the one used. If the last trunk is used as in this case, relay 111will close a contact in the chain of the trunk busy relay 103 circuit toground to indicate that all the trunks are busy as hereinbeforedescribed. Relay 103 is operated over the circuit through the upperouter armatures, and. front contacts of relayssuch as 105 and 111 andintermediate corresponding relays to,

ground. .Itshould be noted that when relay 5 236 operates andtransferstheconnection from the line circuit to the trunk circuit forthe calling subscribers line,'the line switch 204wilibe released andreturned to normal by the release of relay 201 andther'elays conof'relay 140 thus causing the ringing tolbe tripped in the centralofiice.

trolled thereby as hereinbefore described.

Referring now to calls incoming from centraloliice over trunk 101,'whenthe central office seizes this trunk, relay 132 operates and causes theoperation of relay 133. This relay in operating causes the operation ofrelay 111 to prevent outgoing calls from be.- ing 'made over this trunk.7 When ringing current, is applied to the trunk at central OiTlCQ, relay135 operates. This relay in operating closes a circuit for the operationof relay 125 over an obvious circuit. Relay 125 closes a circuit for thetrunk signaling bell 240 as follows: battery, bell 240,1ower armatureand front contact of relay 125, to ground at the upper inner armatureand front contact of relay 135. Bell 240 may be located at anyconvenient place in the private branch exchange where it can be heardfbyany subecriber so that-any SHbSCribeKlnEL-y answer a his call. Relay 125also closes a circuit for relay 112 from battery, winding of relay 112,

upper outer armatureand frontcontact of re 125, to ground-atthe secondupper arma ture and back contact of relay 115. Relay 112 in operatingcloses connections through the trunk connecting circuits toleads 241 and242 from the line circuit in Fig. 2 to control the switchllQO to huntfor the line of the private branch exchange subscriber; that answersthis call. l I

its anysubscriber may answer th1s call and to answer it the subscribermust dial the code 08which will operate the asso-' ciated line switch104 in case the subscriber 200 has answered the call, to cause'thebrushes of this switch to advance to terminal 18. The operation oftheline circuit is the same as hereinbefore describedexcept that in thiscase when the terminal 18 is reached relay 109 is operated with thestart relay 114, instead of relay 108, over the circuit establishedthrough the lead 241, the 18th terminal of bank 205 and the contacts ofrelays 213 and 55 203. In this case the circuit from the start relay 114to conductor 241 is established due to the operation of relays 111 and112 and 'may be traced through the upper armature and front contact ofrelay 112and makebefore-break contacts of relay 111. Therest of thecircuit is the same as-hereinbefore described. The switch' 100 will, dueto the operation of relay'114, start to operate and hunt for the callingline 200 in the same manner as hereinbefore described. Relay 140 will.oper'ate' on the operation of relay 114 from battery,-winding of thisrelay and its make-before-break contacts, second upper armature andfront contact of relay 125,11pperinner armature and front contact of relay 114 to ground. Relay 140 operates simultaneonsly with relay 123 andcloses a locking closes, a circuit for relay 126 through the centraloffice loop and causesrelays 127, 128 and 129 to operate as hereinbeforedescribed.

' When the-switch 100 finds the calling line, 'relays119 and 115 willbeoperated to con: nect the 'subscribers line 200 to the trunk 101 tothe'central oflice. On'the operation'of relay 115', relay 112 willreleaseso that other;

calls maybe answered. e

To transfer trunk calls from one subscriber to another subscriber, it'isnecessary to hold the trunk operated, call the station to whom the'callis to be transferred, release the first connection and have thesubscriber at this station dial a transfer code'n'umber: to pick up thecall on thetrunk. This holding of the trunk is accomplished byoperation. of the holding key 243 at the connected station.

The operation of this key closes a circuit for a conductor 143 which is1 connected through brush144 to'the winding of relay 145 The circuitmaybe traced from batteryiwinding This bridge of relay 145, lowerarmature andback .con-

tact-of relay 113, brush 144, first terminal of this bank, conductor143, upper inner armature and front contactof relay 236, key

243 to ground: Relay 145 operates in this circuit and causes theoperationof "relay 147.

' This relay in operating opens-the connection for the tip conductor andbridges itself across the trunk and through its upper armature and frontcontact and upper Winding through a. resistance 148. Relay 130 alsooperates'over an obvious circuit due to the operation of relay145torelease relays 115, 119, 236and111. The connection from ground at thearmature an'd front contact of relay 129 for these relays is opened atthe upper outer armature andbackcontact of relay 130. When key 243 isreleased relay 113' operates in series with relay 145' from batterythrough the windings of relays 145 and 113, upper outer armature andfrontcontact of relay 145 to ground at thelower armature and front contactof'relay 147. 'Relay113 closes connections for leads 250 and 251 toprepare-for the seizure of trunk 101; ,The'release of the relay236causes the switc'h'204 of the line 200 tc 'be returned to normal. v i1 3 The station; for which the call was intended may now pick uptheltrunk by dialingthe codenumberfOl): The-switch of'this subnects' the*relay to the station. Relay 146 is operated and 7 scribed calls. Thestart relay 114 will now cause the switch to connect with the callingsubscribers line as hereinbefore described. When relay operates it con-146 in series with the trunk closes the circuit through the upperwinding of relay 147 in series with the trunk to the station, thuscausing this relay to release to complete :the connection through thetip to the station and the trunk and short circuit relay 146. Thestation and the trunk are now connected as hereinbefore described. Thesubscriber at this station may also transfer the call in the same mannerto another subscriber. Relay 147 in releasing causes the release ofrelays 146 and 113. Release of 113 releases 110 and 102.

If Fig. 3 is used with Fig. 2 instead of Fig. 1 the operationsof thecircuits in Fig. 2 are the same for outgoing calls over trunk 301 usingswitch 300. Incoming calls and transfer of calls, however, are somewhatdifferent. In case of incoming calls the only difference is that whenrelay 325 operates it closes a circuit for the operation of relay 3'45.This relay in turn closes the circuit for the trunk bell 240 from theground at relay 335iinstead of relay 125 as in Fig. 1.

In case of the transfer of a call the calling subscriber at 200 willdial 0 to hold the trunk 301 forselection by another station in pickingug'the trunk, and to release the switch 20L 1 11 other words, theoriginally calling subscriber dials a number instead of operatingthe ke(243). When this subscribers station is rst connected to trunk 301 acircuit will be completed for the operation of relay 350. The circuitfor this relay 350 incomplete from the calling subscribers loop, the tipand ring conductors through banks 352 and 353, the two upper outerarmatures and front contacts of relay 315, winding of relay 350 tobattery and ground at the central ofiice over the tip and ringconductors of trunk 301. Relay 350 closes acircuit for the operation ofrelay 351. When now the subscriber dials the number 0 these-two re- 1lays will respond to the pulses by releasing sis and-operating. Relay351 when first released will close a circuit for relay 354 and theretery magnet 355 for operation of switch 356. This circuit may betraced from battery, winding of magnet 355, second upper armatlu'eandfront contact of relay 315, winding of relay 354, lower outer armatureand front contact of relay 345, armature and back contact of relay 351,to ground. Relay 354 opcrates-and remains operated during the pulsing.and the rotary magnet 355 in responding to the pulses advances thebrushes of switch 356 to'the tenth position. When the pulsing iscompleted relay 354 releases and causes the operation of relay'357 overa circuit from battery, winding of this relay, lower inner armature andfront contact of relay 345, the tenth terminal and brush of bank 358,lower armature and back contact of relay 354, upper armature and backcontactof relay 359 to ground. Relay 357 in operating closes a circuitfor relay 347 over a circuit as follows: from trunk 301 over tipconductor, upper outer armature and front contact of relay 357, windingof 347, middle upper armature and front contactof relay 357 to the ringconductor back to trunk 301. Relay 347 is now bridged across the tip andring conductors in series with relay 350 over a circuit from the tipconductor, upper armature and front contact and winding of relay 347,lower inner armature and back contact of relay 346, winding of relay 350to the ring conductor. The trunk is hereby held for seizure by anothersubscribers station. Relay 347, also opens the tip conductor for thetrunk at its upper armature and back contact and closes it to the rinconductor. Relay 347 also closes a circuit or the operation of relay 330which in turn causes the operation of relay 313 in practically the samemanner as hereinbefore described in connection with Fig. 1 for theoperation of the relays 130 and 113 except that in this case theserelays are not controlled by relay 346 but directly by relay 347. Thestation 200 connection is thereby released by the opening of theconnection to ground relay 236 with the consequent release of switch204. When relay 354 was released it also closed a circuit for theoperation of relay 359 from battery, winding of this relay, brush ofbank 360 and the tenth terminal thereof, upper armature and back contactof relay 354, to ground at rela 329. This opened the circuit for relay357 and causes the switch 356 to be stepped back to normal positionthrough the circuit completed through the interrupting contacts of thestepping magnet 355, the lower armature and front contact of relay 359,to round at the armature and front contact 0% relay 351. When'the switchhas returned to normal this circuit is opened at bank 360. It-should benoted that relay 359 is slow to operate to permit the circuit for relay357 to be closed before-the switch 356 begins its return to normal andrelay 357 is slow to release so that it will:hold long enough to permitrelay 347 tzpperate and-lockup under control of relay 3v .Anotherstation may now seize the trunk bydialing the proper code, that is, thecode number 08. The operation of the circuit of Fig. 3-in seizing thetrunk 301 by the second subscribers station is similar to the operationof the circuits of Fig. 1 in this respect. The only exception is thatwhen relay 346 opcircuit for switch 356. The reniainin relays andapparatus in the trunk connecting circuit shown in F 1g. 3 have beennumbered with numerals corresponding to the nurnbers have been changedto S insteadotL 9 with Fig.1 or 3 theoperation oi the c" 9. tion withFigs. 1 and 3.

shown in Fig. 1 except that the hundred digits This will aid in'tracingthe 'cuitsin connection with the previous descriptions relatingtothe incoming and outgoing calls. v if. Figs. -i and 5 are used asshown in in establishingv connections from cali -..g sub scribers at 400or- 500 toa trunk 101 or 301 or froni these trunks to. the subscribersare the same as when Fig. 2 is used in conn c- The only difference inthis caseis the method of extending calls between subscribers at theprivate branch exchange. instead of employing relays such asrelaysQQ'T.S250. 251*and 232 as shown-in Fig. 2 forextending this type ofconnections the step-by-step line switches 1-50 for the sub scriber 400and 550'for the subscriber at 500 are employed.

A description for extending a connection between the subscribers. at 400and 500 WLl now be made with the subscriber at 400 as the callingsubscriber. l/Vhenthis subscriber re moves his receiver frointheswitchhook, relays e01, 402 and 403 are operated in the same manner ashereinbeforedescribed i connec tion with Fig, 2 to prepare the pulsingcircuit for the rotary magnet e09, to make the s tion busy by groundingthe conductor and to send out dial tone to the calling station throughthe condenser 422 over the ring conductor. During the dialingof thedesiregtlsubscrib ers number relay 01 follows the pulses andcloses aconnection to ground t" the relay 103 for the operation oi relay andmagnet 1 9 to advance the brushes of switch 450 over the terminals ofthe corresponding banks until the desired subscribefis line is found. ifthe subscriber at 500 is desired the switch will merely take two steps,

' to make the connection. Relays 412 will remain operated during thediali g to keep the test circuit open and prevent the relay 4.13 fromoperating while the switch is in motion. llQreleases at theend of theseries of impulse and relay dl3'is connected. to brush 407. If thecalled line is idle r lay e13 will be connected in series with relay 517in the called line circuit. Both relays operate and relay 517 closes aringing c'rcuit 'froins'oure 595 to-call the subscriber at 500. Rela :13

UAJL/ in operating connects its upper winding through the winding, ofrelay and the brush oiban'k5e, over conductor e56 throughthewinding'oilrelay. 551 to battery. I Relays and551 ,operatein thiscircuit. Belay 51? will test busy to other calls I are used with Fig.

alsocloses a circuit for relay'502, while relay 503 connects busy tonefrom common source 511 to lead 556 so that the called l ne ate'd throughthe chcuit complete at its armature anorfront contact under control or"the ringing relay holds relay 51'? e When the called station answersrelay 526 operates and releases relay 517 thus disconnecting th ringingcausesfror the tip'conductor which is now completed at the upper. outerarmature and back contact of this relay. il hen relay 453 operates itcloses a circuit for the operation of relay 460. This relay in operatingconiplet s the connection between the two subscribers lines overcondensers 459 through the brushes of banks 105. and 4-06 and condensers461. i Talking battery is supplied through the relays 4:01 and 501 tothe calling subscribers and the called subscribers lines respectively.When relay 501 is operated on the release of relay 517 relay 502 ismaintained operated to hold'relay 503 operatedior maintaining of thecalled subscribers line busy. V o

The relays and apparatus in Figs. i and 5 for extending outgoing trunkcalls or calls incoming from trunks have been numbered withnunieralscorresponding to the numeral for the same relays apparatus in Fig. 2with the exception of; the undred digit-s which have been changed to forFig. v5 to 5. As stated, lligs and 5 may be used with eitherl ig. 1 or 3and in trans ferring calls it they are user the key 442 or 542 may beused'or if they 3 the subscriber at station 400 or 500 will dial thetransfer codenuniber to hold the trunk. I i

Referring now to Figs. 6 and? arranged as shown in Fig. 10, thesecircuits are equipped Relay 551 now with" Fig. .1

propercode number and in this case the trunk on which the call iswaiting will be automatically seized by hi" ing increments of the,switch. Calls may be transferred by actuating a keyat the connectedsubscribers station and the switch thereby released and the trunk held.ilny station niayjthen pick up the call by dialing proper code numberand automatically select the tru Referring "now to the drawings, .1 igs.6" and 7, three subscribeis.l1nes have been shown at 600, 700 9.1151701respectively with the r; associated selector connectors 02, 703 and 704respectively. Only'the circuits for the subscribers line 600 have beenshown in detail in Fig. while the circuits for the other subscribershave merely been indicated by boxes 705V 706 respectively. in Fig. 7 thecircuits of one trunk line have been shown.

It should be noted that in these selector counectors the first level hasbeen assigned for seizing trunks on transfers, the second level has beenassigned for seizing trunks on incoming calls and the third level hasbeen assigned for seizing trunks on outgoing calls, while the remaininglevels have been assigned for local connections.

The operation of the circuits in extending a call from one privatebranch exchange subscribe! to another will now be described. It thesubscriber at 600 removes his receiver from the hook, relay 601 isoperated over a circuit completed through the subscribers loop and thetwo windings ofrelay 601. The operation of this relay closes an obviouscircuit for the o 'ieration of relay 602 and this relay in turn closes acircuit for the operation of relay 603. Bela y 602 closes a connectionto ground at its upper outer armature and front contact, through thelower inner armature and back contact of relay 60%, to the sleeveconductor connected to the terminals of this line in the variousselector connectors so as to make this line test busy. Tone from thesource 606 will be transmitted to the calling subscriber to indicatethat the switch is in working condition and that dialing of the desiredsubscribers line may be begun. When the calling subscriber dials thefirst digit relay 601 follows the impulses and closes a connection toground for the operation of relay 607 in series with the vertical magnet608. This circuit may be traced from battery through the windings ofmagnet 608 and relay 607, second lower armature and front contact ofrelay 603, vertical cit normal contacts 609, upper inner armature andfront contact of relay 602, to ground at the armature and back contacto'l relay 601. The first stop of the brushes 707, of switch 702, changethe connections at the vertical olt normal contacts for the pulsingcircuit which now passes through the make contacts of the vertical offnormal contacts. lower inner armature and front contact of relay 603 andthe lower armature and front contact of the relay 607 that remainriioperated during the pulsing. The change in the position of the verticalot'f normal contacts also cuts off the dial tone.

When the first series of pulses ceases relay 607 releases and a circuitfor the rotary magnet 610 will then be completed for control by thesecond digit impulses as follows: battery, winding of the rotary magnet610, fourth low er armature and back contact of relay 611, upper innerarmature and back contact of relay 612, third lower armature and backcontact of relay 613, lower armature and back contact of relay 607,inner lower armature and front contact of relay 603, vertical of! normalcontacts 609, inner upper armature and front contact of relay 602, toground at the armature and back contact of relay 601. This circuit fromground at relay 601 is also completed through the lower outer armatureand back contact of relay 611, through winding of relay 614 to battery.Relay 614 also operates on the first impulse and closes a circuit foritself through its upper armature and front contact, third lowerarmature and back contact of relay 613 to the ground for 601, independent of the path through armatures and contacts of relay 611. Relay614 remains operated during this series of impulses. When relay 614operates a testing circuit for relay 612 is closed to the sleeve brushof switch 702 from battery, winding of the release magnet 615, lowerwinding of relay 612, armature and back contact of rotary magnet 610,lower outer armature and front contact of relay 614, lower innerarmature and back contact of relay 613 to the sleeve brush.

lVhen the switch stops relay 612 will test the line called and if theline is idle will remain unoperated. The relay 614 will then release andthe upper winding of relay 611 will be connected to the sleeve brushover a circuit as follows: from ground, lower outer armature and frontcontact of relay 602, upper outer armature and back contact of relay612, upper winding of relay 611, make-beforebreak contacts of relay 614,lower inner armature and back contact of relay 613 to the sleeve brush.This relay 611 operates partially over this circuit in series with arelay corresponding to relay 616, in the called subscribers circuit. Thecircuit for this relay may be traced from battery, winding of thisrelay, upper outer armature and back contact of the relay correspondingto relay 602, lower inner armature and back contact of the relaycorresponding to relay 604 through the sleeve terminal on the switch702. The partial operation of relay 611 closes a connection through itssecond lower armature and front contact causing it to fully operatethrough its lower winding over a circuit from battery through thiswinding, second lower armature and frontcontact to ground at the innerlower armature and front contact of relay 602. Relay 611 in operatingfully establishes a ground connection for the sleeve and causes theoperation of the relay corresponding to relay 616 in the calledsubscribers circuit. The ground connection is established directly fromthe ground at the outer lower armature and front contact of relay 602through the'third lower armature and front contact of relay 611 to thesleeve. The operation of the relay corresponding to relay 616 closes thetalking connection from the called subscriber to the tip and ringterminals of switch 702 on which the brushes 707 are resting. Ringingcurrentis nowapplied to the of relay 611, upper outer armature and backcontact of relay 604, lower armature and back contact of relay 618 toground; The calling subscriber will hear the ringing from the toneintroduced in the upper winding of relay 618 over a circuit through thesecond upper armature and front contact of relay 603, upper winding ofrelay 613, condenser 620 and upper make-before-break contacts of relay604, upper outer armature and back contact of relay 616, to the tipconductor of the call- 4 ing subscribers line. 1 Y

When the called station answers this call, current through the lowerwinding of relay 618 causes this relayto operate and connect the. linestogether through the condensers so 620 and 621, over the lower armatureand front contact and upper inner armature and front contact of thisrelay; Talking battery is supplied through the windings of relay 601 forthe calling subscribers line and through the winding of relay 613 forthe called subscribers line. The circuit I from battery and groundthrough the winding of relay 601 has already beendescribed and thecircuit from battery and ground through the winding of relay 613 areobvious. Relay 618 in operating provides a locking circuit for itselfthrough its upper outer armature and front contact to ground at thelower outer armature and back contact of relay 604 I under the controlof relay 603.

When the calling subscriber hangs up his receiver, relays 601, 602 and603 are released causing the release of relays 618 and 611 and thecircuit for the release magnet 615 is closed from battery winding ofmagnet 615, inner lower armature andv back contact of relay 603,vertical off normal contact 609, upper inner armature and back contactof "relay 603 armature and back contact of relay 601 to ground. lVhen.the switch 602 has been returned to normal the vertical off normal 7contacts 609 open the circuit for the release magnet. V.

If the called station had been busy when the relay 612 made the testthesleeve terminal on the called subscribers circuit would have beenconnected to ground as hereinbefore described. Relay 612'would haveoperated and thus prevented the operation of relay 611 when relay'614released; and a busy tact of relay tone would have been sent to thecalling, sta

tion from the source 623 through the circuit I completed at the. lowerarmature and front contact of relay .612, upper inner, armature and backcontact of relay 613 through the condenser 620 to thecalling-subscriber.

To make a call to a central ollice the call-. ing subscriber dials theoutgoing trunk code number. 'In'this case this number would be :whichwouldrbring the switch 702 to the third level. he switchwillbe-operated-as hereinbefore described in connection with the stationto station'call; When the brushes arrive at the third level ahuntingwill'be started for an idle trunk to the central oflice. This isaccomplished by havingoffnormal springs 622 so arranged that they willbeclosed by the switch when the third level is reached. The closing ofthis switch causes relay 613 to operate over a circuit as follows: frombattery lower winding of relay 613, upper make-before-break contact ofrelay 618, low.- er inner armature and back contact of relay 611,contacts 622, to ground at the lowerarmature and front contact ofrelay602. A circuit will then be closed for the operation of relay 612as follows 5 battery, winding of the release magnet 615, lower windingof relay 7 612, armature and back contact of the rotary magnet 610,lower outer armature and'front contact of relay 613, eleventh steprotary ofi' normal contacts 625, contacts 622, to ground at the lowerouter armature and front'con- 602. i y t Then the relay 607 releasesafter the verti cal impulseshave been transmitted circuits are completedfor the operation of the rotary magnet 610 and relay 614. These circuitsmay be traced from caller through the windings of the magnet and relayin parallel through the two lower armatures and back contacts ofrelay'611, upper inner armature and front contact of relay 612, upperarmature and back contact of relay 607, second lower armature and frontcontact of relay 613, contacts 622, to ground at relay 602. Theoperationof the rotary magnet in operating opens the energizing circuitfor relay 612 which now releases. Relay 612' in releasing opens thecircuit for therotary magnet and relay 614. Rotary magnet releases andrelay 614 remains operated for a short period as it is slow'to release..Relay 612is nowj through the lower armature and back contact of relayssuch as relay 708, resistances such as 707 and upper outer armature andback contact of relays such as relay 710. The switch 702 will thereforestep in this manner until an idle trunk is found when the relay 612'isenergized over its upper winding in the following manner: Assuming thattrunk 711 is idle relay 612 will not release but will be maintainedoperated from the battery at relay 708 before relay 614 is released overa I circuit as follows: battery, lower armature relay 613.

and front contact of relay 708, resistance 707, up r outer armature andback contact of re ay 710, the sleeve terminal of trunk 711, sleevebrush of switch 7 02, lower inner armature and front contact of relay613, upper Winding of relay 612, lower inner armature and front contactof relay 614, upper winding of relay 611, upper outer armature and frontcontact of relay 612 to ground at the upper outer armature and frontcontact of Therefore when the switch 702 finds an idle trunk having abattery connection on the sleeve the relay 612 is held operated overthis circuit to prevent further stepping'of the switch. Relay 611 isalso partially operated over this circuit and to close the circuitthrough its lower winding to cause it to be fully operated ashereinbefore described. Relay 611 opens the circuit for the rotarymagnet and relay 614 and closes an obvious circuit through contacts 622for the operation of relay 604 which prevents ringing current from beingconnected to the trunk. I Relay 604 also transfers the talkingconductors of the calling station directly to the trunk through itsupper armature and front contact and the trunk connection is completedthrough the upper a-rmatures and front contacts of relay 611. When relay604 operates relays 601 and 602 are released and the control ground forrelays 611 and 603, is transferred to relay 604 lower outer armature andfront contact. Relay 602 however releases relay 613 and this relayreleases relay 612, whereas relay 604 is held from a ground connectionon the sleeve established at trunk 711 as soon as the talking conductorsare extendedto this trunk. How this ground is applied will presently bedescribed. Relay 604 also applies a busy ground on the sleeve conductorfor the calling subscribers sleeve terminals at the selector connectorswitches to make this subscribers line test busy. If all of the trunksare busy the switch will stop on the eleventh rotary step at which timethe contacts 625 are operated to stop the switch by opening the rotarymagnet circuit and to connect busy tone from source 623 to the callingstation.

when the talking conductors are extended through to the selected trunk711 relay 712 will operate from battery winding of this rela upper innerarmature and back contact 0 relay 713, over the loop completed throughthe-calling subscribers station back over the tip conductor through theupper armature at its lower inner armature and front contact a to holdthe switch 702 actuated by completing the circuit for relays 604 priorto the opening thereof by the release of relay 602 as hereinbeforedescribed. This circuit may be traced from battery, winding of relay604, lower inner armature and front contact of relay 611, contacts 622,third lower armature and frontcontact of relay 611 to the sleeveconductor, through the sleeve brush of switch 702,.sleeve terminal oftrunk 711 to ground at the lower inner armature and front contact ofrelay 712. The sleeve terminal of trunk 711 will therefore also be madetotest busy to other switches. Relay 7 12 in operating closes obviouscircuits for the operation of relays 715 and 716. Relay 715 in operatincloses an obvious circuit for the operation 0 relay 710. Relay 716 inopcratingopensthe shunt circuit for relay 717 and closes a bridgecircuit for the trunk at its. inner and middle lower armatures and frontcontacts. This bridge is also connected to ground through a resistance718 over the upper outer armature and back contact of relay 708 and makebefore break contacts of relay 719 and serves to signal the centraloffice.

lVhen the central ofiice answers, this signal relay 717 operates. Thetip conductor of the trunk at the central office is normally opened sothat relay 717 will not operate until the central ofiice operatoranswers. \Vhen neliay 717 operates it closes a circuit for the operationof relay 719 and this rela in operating opens the connection to grouncfor the trunk conductors and closes a circuit for the operation of relay7 08. Relay 708 opens the original battery connection to the sleeve atthe switch 702 and closes a locking circuit for itself under control ofrelay 715. Relay 713 is also operated by the operation of relay 719 andconnects the tip and ring conductors from the calling station to thecentral oflice and opens the circuit for relay 712 which releases and inturn causes the release of relay 716. Relay 715 does not release but isheld operated from the ground connected through the lower armature andfront contact of relay 719 over lower inner armature and front contactof relay 713. Relay 716 in releasing closes the shunt circuit for relay717 through resistance 720, but this resistance is of such character asto permit relay 717 to remain operated and is inserted as is well knownin the art to improve the transmission characteristics of the talkingcircuit with the relay 717 still included therein. The ground connectionfor holding the switch 702 is now provided from theground at the lowerouter armature and back contact of relay 721 through theuppe riouterarmature and front contact of relay 710 to the sleeve.

- On incoming calls from the central orlice when trunk 711' isseized-relay 722 is operated over the connection completed through thetip and ring conductors over the lowerouter armature and back contactsof relay 713 and upper outer armature and back-contact of relay 716.This relay closes an obvious circuit for the operation of relay 715which closes a circuit for the operation of relay 710 to connect groundto the sleeve terminals of the trunk at the second level of the switcheswhich areassigned for extension of incoming calls. This groundconnection may be traced from the ground at the lower outer armature andback contact of relay 721, upper outer armature and back contact ofrelay 723, lower outer armature and front con tact of relay 710 to thesleeve terminal of this trunk in the second level. This groundconnection is also applied to the sleeve tenninals ofthe trunk at thefirst and'third' levels to make the trunk busy. The ground for thesleeve at the first level may be traced'th'roguh the upper outerarmature and front contact of relay 710, and for the third level throughthe upper inner armature and front contact of relay 710 and the lowerinner armature and back contact of relay 721. When new ringing currentis applied at thecentral of fice' over the Y tip and ring" conductorsthe alternating current responsive=relay725 operates to provide a;circuit for'holding relay 715o'perat-ed and'a circuit foroperating relay723. This latter circuit may be tracedfroin battery, the'winding ofrelay 723,'lower outer armature and back contact of relay 712,make-before-break contact of relay 723, second upper armature and frontcontact of relay 710, to ground at the upper armature and front contactof relay 725. Relay 723 closes a holding circuit for itselflthrough itsupper inner armature and front contact toground at the inner lowerarmature and front "con tact of relay 710. Relay 723 establishes a'connectionfrom battery, lower armature and back contact of relay 708,resistance 707; upper outer armature and front contact of relay, 723,lower outer armature and front contactv of relay .710 to the sleeveterminal of the trunk at the second level ofeach selector-connectorswitch." This battery connec tion will now identify the: incoming trunkon theswitch-of a subscriber answering this call to cause the switch tostop and cut in on I the trunk.- The operation'of relay 723 also closesthe, circuit for the private branch exchange signal 726 which may belocatedin ariyconvenient place in the exchange; The circuit for thissignal may be traced from battery, winding of the signal, inner: lowerarmature and front contact of relay 723, sec- 0nd upper armature andfront contact of relay 710 to ground at the upper armature and frontcontact of relay 725.

*When this signal is heard at the private branch exchangethe subscriberat any station'may answer the call by dialing the'incoming centraloifice code which. in this case will be 2. "The switch of the callingsubscriber will now advance. its brushes to this level and hunt overthis level until the calling trunk is reached. It should be noted i thatin this case trunk 711 is provided with battery orrthe sleeve terminalat the second level, while the sleeve terminals of idle trunks on thislevel are open and busy trunks are grounded. The trunk is thereforeseized b a callin subscriber in the usual manner {7 and the usualcircuit changes will take place to again, apply the ground on thissleeve terniinal to make the trunk test busy. Relay and front contact ofrelay723, to ground at the lower outer armature and front contact ofrelay 716. Relay 727' in operating con nects at its upper armature andfront contact, relay717 across the tip and ring conductors towards thecentral oliice thus tripping the central ofiice ringing after whichrelay 717operates and causes the circuit'to function as hereinbeforedescribed in cone nection with outgoing calls. Relay 713 in operatingdisconnects relays 722 and 725 from the trunkand rel y 715 is heldoperated by relay 719.

If a call is to be transferred from one subscribers station to anotherthe connected subscriber will operate the transfer key 630. Theoperation of this key establishes a connection to ground for the fourthterminal of the connecting trunk. 'It is immaterial the three levels areall connected together.

The ground applied by key 630 causes the release of relay 728. It shouldbe observed that relay 728 always operates whenever relay 710 isoperated causing also the operation of relay 729 over obvious circuits.The release or relay 728 causes a circuit to be closed for the operationof relay 714, from battery lower winding of this relay, upper armatureand front contact of relay 729, armature and back contact of relay 728,to ground at armature and front contact of relay 715. This circuit ispossible due to the slow-.to-release characteristics of relay 729. Relay714 in operating closes its upper winding across the tip and ring:conductors through its upper armature and front con ios tact andthereby maintains itself operated and holds the trunk at the centralofiice. When relay 729 1 eleascs a connection is closed for theoperation of relay 721 as follows: battery, winding of relay 7 21,make-beforebreak contacts of relay 729, upper armature and back contactof relay 728, to ground at relay 715. Relay 721 in operating provides alocking circuit for itself under control of relay 714 and opens theholding ground over the sleeve terminals for the switch of the connectedsubscribers line, thereby causing the switch to release and disconnectthis line from the trunk. lVhen the holding key is restored to normal,relays 728 and 729 are again operated so that the call may be againtransferred if so desired.

-This trunk, it should be noted, will now have a battery connected toits sleeveterminals, at the first level, due to the operation of relay721 and reoperation of relay 729. The trunk may therefore in the usualmanner be picked up by any of the other stations by the dialing of thislevel and'the hunting for the trunk thus identified. When the trunk isseized by another station at the private branch exchange a relay 730 isoperated as the winding of this relay is now connected in series in thetip conductor through the upper outer armature and front contact ofrelay 720. The operation of relay 730 shunts the upper winding of relay714 which now releases and closes the connection through the tip to thecentral oiiice from the calling station. Relay 714 in releasing causesthe release of relay 721 which again establishes a connection to groundfor the sleeve terminals of this trunk to hold the connected switch andmake itself busy.

While this invention has been described in connection with a limitednumber of circuits, it should be understood that it may be applied inmany other systems without departing from the spirit thereof.

What is claimed is:

1. In a telephone system, subscribers lines, trunks, means including anautomatic switch for connecting a subscribers line with a trunk, meansfor releasing said subscribers line from said trunk and for marking saidtrunk,.and means for thereafter connecting a subscribers line with saidmarked trunk over said automatic switch.

2. In a telephone system, subscribers lines, trunks, means including anautomatic switch for connecting a subscribers line with anothersubscribers line or with a trunk, means for releasing a subscribers linefrom a trunk to which it is connected and for marking said trunk, andmeans for thereafter connecting a subscribers line to said marked trunkover said automatic switch.

' 3. In a telephone system, subscribers lines, trunks, means includingan automatic switch for connecting a subscribers line with a trunk,

means for releasingsaidsubscribers line from said trunk, for markin saidtrunk and from holding it engaged ant means operative due to themarkings of said trunk for thereafter connecting a subscribers line withsaid marked trunk over said automatic switch. I

4. In a telephone system, subscribers lines. trunks, automatic switchingmeans for causing the connection of a subscribers line with anothersubscribers line or with a trunk over a path excluding said automaticswitching means, means for opening the path connecting said subscribersline and said trunk and for marking said trunk, and automatic switchingmeans for thereafter causing the connection of any subscribers line withsaid marked trunk over a path excluding said last mentioned automaticswitching means.

5. In a telephone system, a first and a second ofiice, subscribers linesterminating at the first oflice, trunks connecting said ofiices,automatic switching means for connecting a subscribers line with a trunkseized at the second office, means for opening the connection betweensaid subscribers line and said trunk and for marking said seized trunkat the first oflice, and an automatic switching means for thereafterconnecting any subscribers line with said marked trunk.

6. In a telephone system, a first and a second oflice, subscribers linesterminating at the first office, trunks connecting said ofiices, meansres onsive to the setting of the switch at any su cribers line forconnecting said line to an idle trunk or to a trunk seized at the secondofiice, means for releasing a subscribers line from a seized trunk andfor marking said trunk and means responsive to the setting of the switchof any subscribers line for connecting said line with a marked trunk.

7. In a telephone system, a first ofiice and a second office,subscribers line terminatin at the first oflice, a switch associatedwith eac subscribers line, trunks connecting said offices, meansresponsive to dialing impulses received from a subscribers line forsetting the corresponding switch to cause the connection of saidsubscribers line over a path exeluding said switch with anothersubscribers line or with an idle line or with a trunk seized at thesecond office, means for releasing a connection to a seized trunk andmarking said trunk and means responsive to dialing impulses receivedfrom a subscribers line for setting the corresponding switch to causethe connectionof said subscribers line over a path excluding said lastmentioned switch with said marked trunk.

8. In a telephone system, a. first oflioe and a second office,subscribers lines terminating at the first oflice,a switch associatedwith each subscribers line, trunks connecting said oil-ices, meansresponsive to dialing impulses received from asubscribers line forsetting the corresponding switch to'cause the connection of saidsubscribers line over a path excluding saidswitch with anothersubscribers line or with an idle trunk'or with a trunk seized at thesecond 'oifice, means for releasing a connection to a sized trunk andmarking said'trunk responsive to dial impulses from the connectedsubscribers lines andomeans responsive to dialing impulses received froma subscribers line for setting the corresponding switch to cause theconnection of said subscribers line over a path excluding said lastmentioned switch with said marked trunk. l

9. In a telephone system, a first ofiice, a second ofiice, subscriberslines terminating at V the first ofiice, a switch associated with eachfor setting the switch of'any subscribers line to cause a connectiontobe established over a pathexcludlng sald last mentloned switch betweensaid subscribers line 7 and said p p thesecondoificehmeans for releasinga conmotion to aseizedtrunk and marking said marked trunk. I o i 10. Ina telephone system, a first oifice and second oilice, subscribers linesterminating at the first office, aswitch associated with eachsubscribers line, trunksconnecting said ofiices, means responsive todialing impulses received from a subscribers line for actuating thecorrespondingswitch to connect said subscribers line with anothersubscrib crs line through said switch or for setting said switchto causethe connection of said su'bscribers line over paths excluding saidswitch with an idle trunk or with a trunk seized at the second office,means responsive to impulses received from a subscribers line connectedto a seized trunkfor releasing said connection and marking said trunkand means responsive to dialing impulses from any subscribers line forsetting the corresponding switch to cause a connection to be establishedover a path excluding said last mentioned switch between saidsubscribers 7 line and said trunk.

11. In a telephone system, subscrihers hnes, a switch for eachline,trunks, aswitch for each trunk, means responsive to the set ting of theswitch of any subscriberls line for actuating the switch of an idletrunk or of a seized-trunk to connect said trunkto said subscribersline, means for releasing the connection between a suhscribers line anda seized trunk andv from marking said trunk and means responsive to thesetting of the switch of any subscribers line for actuating theswitch'ofsaid markedtrunk toconnect said trunk to the last mentioned subscribersline. i i l 12.. In a telephone system, callingsubscribers lines aflineswitch for each line, trunks,

a" switch associated with each trunk, means responsive to theselectionof certain terminal points-on. the line switch: by dial;impulses r'eceivedover the associated subscribers line for actuating theswitchof an, idle trunk to connect said'trunk'with said subscriberslineor for actuating the switch of a seized trunk to connect said trunk withsaid, subscribers line, means formarking said seized trunk and forreleasing it from said subscriber-ls line and: means responsive to theselectlon of a .certaln other terminal point on the line switch ofanother subscribers line by: dialing impulses-receivedover said othersubscribers line for actuating the switch of said marked trunk toconnect said trunk to said other subscribers line. 7 o

13. In a telephonesystem, a first ofiice and a'secondofiice, subscriberslines terminating 1 at the first oflice, trunks connecting saidooffices, a'connector switchfor each subscribers line, means responsiveto the'actuation of the switch of any subscrlbershne for connectmg thecorres ondin '"-subscribers line throu h said switch with anothersubscribers line or with anidle trunk or-with a trunk seized at trunkand means responsive tothe actuation of the switch ofiany subscrib'ersline for connecting the corresponding subscribers line through saidswitch with a marked'trunk. v

14. In a telephone system, a first office and a second office,subscribers lines terminating at the first office, trunksconneetingasaid, of, fices,-a selector connector switch foreach line,

' means for actuating a switch of a subscribers trunk through said lastmentioned switch. o

15. In a telephone system, a first ofiice and f a secondolfice,subscribers lines terminating at the first ofiice, trunksconnecting said on fices, a selector connector switch for each line,

means responsiveto dialing impulses received from a'subscribers line foractuating the corresponding switch to connect, said subsubscribers linewith another subscribers line or with anidle trunkor with a trunk seizedat the, second oflice, through said switch, means responsive to dialingimpulses received from a subscribers line connected'to a seized

